The　use　of　phase　change　materials　(PCMs)　in　buildings　is　an　efficient　way　to　reduce　the　building　energy　consumption.　PCM　wallboards　used　in　buildings　have　been　widely　studied　and　optimized　in　many　studies;　however,　further　thermal　performance　analysis　needs　to　be　performed.　To　utilize　the　PCM　more　efficiently　in　practical　engineering,　five　PCM　wallboards　used　in　the　exterior　wall　of　an　air-conditioning　room　in　Beijing　were　studied　using　numerical　simulation,　and　four　new　aspects　of　the　thermal　performance　analysis　of　PCM　wallboards　were　presented.　It　was　found　that　the　energy　consumption　of　the　building　using　the　PCM　wallboard　with　a　higher　phase　change　range　was　103　kJ　less　than　the　referenced　wallboard　in　June,　while　72　kJ　more　in　December.　Therefore,　the　thermal　performance　of　the　PCM　wallboard　might　be　adverse　in　different　seasons,　and　the　thermal　performance　analysis　during　an　entire　year　was　necessary.　Using　the　heat　ratio,　the　months　in　which　the　phase　change　had　a　significant　effect　on　the　thermal　performance　of　the　wall　were　found,　and　only　in　these　months,　the　optimization　of　the　thermal　performance　was　effective.　The　heat　transfer　coefficient　of　the　PCM　wall　was　defined,　and　it　was　used　to　justify　that　the　PCM　met　the　design　standard　for　energy　efficiency　of　buildings.　Using　relative　thermal　conductivity,　the　effective　months　of　the　phase　change　for　different　areas　of　China　were　determined.　The　optimization　of　the　thermal　performance　of　the　PCM　wallboard　should　focus　on　these　months.　For　Beijing,　the　months　were　June　and　September.　For　Harbin,　the　months　were　July　and　August.　For　Shanghai,　the　months　were　June,　July,　and　September.　For　Guangzhou　and　Haikou,　the　months　were　May　and　April,　respectively.